The present invention relates to a solid state catalyst process and plant for the abatement of organic compounds including noxious compounds contained in water by enrichment of the water with ozone/oxygen and then contacting the water with a catalyst.
A number of methods are known in the art to substantially or partly remove noxious compounds from drinking water. The usual methods are UV-treatment, absorption on activated carbon and treatment with ozone. In the patent literature, certain catalysts are further suggested for the abatement of organic compounds from water.
UV-treatment is employed to decompose or partly decompose organic compounds by radiation with ultraviolet light. UV-units demand excessive maintenance and are expensive due to high power consumption of about 1 KWH/m.sup.3 water. The UV-radiation tubes must frequently be cleaned due to deposited solids, mainly precipitated manganese and iron oxide. Sediments can be removed with hydrochloric acid.
Activated carbon can be employed in the removal of organic noxious compounds which readily absorb to high molecular compounds. The activity of activated carbon decreases gradually with the amount of absorbed compounds, thereby, causing frequent replacement of active coal loadings.
The amount of active coal used in the loadings depends on concentration of organic material in the water to be treated. Usual retention times in carbon filters of about 15 minutes correspond to about 0.25 m.sup.3 activated carbon/m.sup.3 water/hour. There are no safe data for those units, but the loadings have to be replaced once a year caused by saturation with organic material and biological growth in cleaning vessels, which can form biofilms.
Biofilms may clog the surface, and thus destroy purification properties of carbon.
Ozone is used in a number of units for the treatment of drinking water.
Ozone decomposes some organic compounds partly. Odorous smell is removed. Minor amounts of pesticides are removed by ozone treatment, but ozone is not effective in the removal of all kinds of pesticides and decomposition products of pesticides. Ozonization methods are used in disinfection and removal of smell from surface water in combination with after-treatment with activated carbon.
Catalysts being active in purification of air and water are known in the art.
DE-A-3,149,901 discloses a catalyst for the decomposition of ozone in gases. The catalyst is employed in the removal of ozone from processes, wherein ozone is formed e.g. photo copying, ozonisation units or in the disinfection of water, air cleaning, bleaching, etc, as ozone is noxious in higher concentration (0.2-1 ppm).
Treatment of water with a catalyst, which is not supported on activated carbon is known from EP-A-354,664. This method is not directed to removal of noxious organic compounds, but in removal of smell, in bleaching or sterilization, and to remove excess of ozone from water. The catalyst is composed of one or more compounds from titania, silica, zirconia, manganese, iron, cobalt, nickel, cerium, tungsten, copper, silver, and gold, palladium, platinum, rhodium, ruthenium and iridium.
U.S. Pat. No. 4,029,578 discloses a process for the treatment of drinking water or waste water with ozone and a heterogen catalyst without activated carbon.
The catalyst is composed of at least two compounds of copper, cadmium, iron, cobalt, nickel in a ceramic material of alumina or silica. The preferred catalyst is a mixture of iron and cobalt on alumina.
GB-A-2,089,671 relates to ozone decomposition in air on a catalyst. The preferred catalyst is Pd/Co/alumina. This patent publication discloses gaseous phase reactions and a catalyst based on a ceramic carrier.
Filter units with a material of titania, silica and zirconia or mixtures of these oxides are mentioned in DE-A-2,156,571. Carbon is not disclosed as carrier.
Thus, many methods to purify water are known in the art. Clean drinking water is vital and increasingly rare. In many areas ground water reserves disappear with increasing consumption and pollution. There are many sources of grounds water pollution, including pollution from industrial areas and dumping grounds additionally use of fertilizers and pesticides in farming.
Additional sources are e.g. leaky sewers, emission of waste water or pollution from pipelines or discontinued oil tanks.
Common to all sources of pollution is that they are threatening drinking water quality. To limit these problems different restrictions on waste water discharge and introduction of cleaner technology have been made.
Problems emerging these years, are the result of previous years of fertilizer consumption, use of pesticides and dumping of waste water. It is expected that ground water pollution will increase over the years to come.
In particular, pesticides have very low concentration limits of 0.1 .mu.m/l. Concentration limits are problematic as new compounds enter the market continuously for use in extreme low amounts. As an example, the pesticide chlorosulphuron can be used in amount of 4 g/10,000 sq. meters. In comparison, 1-4 kg atrazine/10,000 sq. meters have to be used, but both compounds have the same limit of concentration.
International investigations have shown that more than 30 pesticides are potentially soluble, whereas present experiments are concentrated towards the pesticides atrazine and phenoxy acids (hormone agents).